If one had 90% formic acid but wanted to make it anhydrous could one just add MgSO4 to remove that last 10% of water then filter?
or use a CaCl2 with desiccator to remove that 10% ?
Thank Youzed - 10-6-2010 at 14:42
I've heard of people using molecular sieves.
I'd approach projects utilizing concentrated Formic acid with some caution. Under some conditions, It may decompose....sort of exploding. I can
remember distilling formic acid out of a Peroxidation product, with some trepidation.
In fact, the water present in 90% Formic acid, serves to stabilize it somewhat.
Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the container it is kept in. For this reason
98 % formic acid is shipped in plastic bottles with self-venting caps.
There may be some good threads on Formic Acid in the archives. Especially, regarding recycling and drying it. It's a common co-solvent in
peroxidation reactions utilizing Acetone/30% H2O2/Formic Acid. The bugaboo being that the Formic acid is expensive, very corrosive, none too stable,
and it hangs on to water. The corrosive and unstable parts, giving one....pause for thought, especially regarding recycling.
If one had 90% formic acid but wanted to make it anhydrous could one just add MgSO4 to remove that last 10% of water then filter?
or use a CaCl2 with desiccator to remove that 10% ?
Thank You
Neither of these works very well.
Anhydrous oxalic acid or anhydrous boric acid acid work well.
It's in the literature. You know, that stuff that people don't read.not_important - 10-6-2010 at 17:15
Anhydrous boric acid is still H3BO3, what is meant is boron oxide B2O3, used for dehydrating formic acid before the advent of molecular sieves. As
entropy51 said, niether CaCl2 or MgSO4 work well. Also, as zed stated, formic acid becomes increasingly prone to decomposition as the concentration
rises above 80% or so, concentrations above 90% should not be stored for long but rather used within a few days of preparation. The decomposition
releases H2O and CO, which will overpressure the container unless vented, unvented containers have been known to burst forcefully.
It works well, the problem is that the traditional way to make B2O3 is to heat H3BO3 on through the dehydrating stage, where it softens and puffs up,
on up to read heat where it melts to a glass, then pour that onto chilled steel sheet (for flakes) or into chilled CCl4 (for pellets). Glass and
ceramic containers react with the hot B2O3, so corrosion resistant metals crucibles were used.
This is all a bit inconvenient, the following is somewhat less demanding and gives a very active form of B2O3. The text is from OCR of scanned images,
you may wish to see those.
While they say to use a "drying pistol over phosphorus(V) oxide", a round bottomed flask works fin; the idea is to have the boric acid in a fairly
shallow layer so that is is easy for the water vapour to escape. The alternative method of passing a slow stream of dry air over the H3BO3/B2O3, but
using just a H2SO4 drying trapped and then adding a finishing stage of continuing to heat under vacuum (air flow cut off) for an hour or two seems to
work. This modified method is similar to that used to regenerate molecular sieves.
7. POROUS BORON OXIDE
2H3B03 => B2O3
SUBMITTED BY WILLY LANGE
CHECKED BY H. s. BOOTH AND FRED E. KENDALLt
When prepared by fusion of boric acid, boron oxide forms
a very hard and tough mass that can be ground only with
great difficulty. However, the anhydrous oxide can be
obtained in a porous form by carefully heating crystallized
boric acid in a vacuum.1 The resulting product can be
powdered readily.
Procedure
Crystallized boric acid is placed in a small vessel in a
drying pistol over phosphorus(V) oxide and dehydrated
completely by heating in a vacuum at 200 C. The vacuum
of the water-jet pump is sufficient, but a better vacuum is
preferable. It is important that the temperature be
raised slowly to 200 C; otherwise, the mass sinters, and
the further escape of moisture is prevented. The larger
the quantities used, the longer heating at 200 C must
be continued, up to4 hours, before dehydration is complete.
For 3 g. of boric acid, 1 hour of heating is sufficient.$.
Properties
Boron oxide obtained from pure crystallized boric acid by
this procedure is a snow-white, porous, slightly sintered
substance. It can be powdered easily, but atmospheric
moisture must be excluded during this operation. The
sintered material is highly reactive and, when wet with
water, evolves heat and hisses, like phosphorus(V) oxide.
Reference
1. TIEDE and RAGOSS: Ber., 66, 656 (1923).
* University of Cincinnati, Cincinnati, Ohio.
t Western Reserve University, Cleveland, Ohio.
# Those who checked this synthesis found that it is possible to dehydrate
boric acid in a current of dry air provided that the temperature is not permitted
to rise above 200". Air, dried by passing it through sulfuric acid, in a
trap, and then through either phosphorus(V) oxide or porous barium oxide,
is passed over the boric acid in a boat or other container in a combustion
tube. The latter is heated in a tubular electric furnace so that a thermometer
placed alongside, but outside the tube, never indicates a temperature
higher than 200'. The exit end of the combustion tube is connected
through a phosphorus(V) oxide or barium oxide drying tube and a trap to
a water suction pump. The air should be passed so slowly that a bubble
rises through the sulfuric acid about every 5 to 10 seconds. This rate of
flow can be attained by a stopcock placed just before the entrance end of
the combustion tube.
If one had 90% formic acid but wanted to make it anhydrous could one just add MgSO4 to remove that last 10% of water then filter?
or use a CaCl2 with desiccator to remove that 10% ?
Thank You
Ullmann (albeit the 5th ed. as I cannot find sufficient
use in the current ed to justify spending a pile of money)
list a number of methods used in industry. One of the more
easily accessible refs is a US Patent.
4 076 594
Purification of formic acid by extractive distillation
Horst Buelow et al
Formic acid is purified by extractive distillation of its aqueous
solutions using a basic extractant, followed by distillation of the
bottom mixture first obtained, the extractant used being
N-formylmorpholine.
Curious
Ullmann notes —
[In part]
Azeotropic data for the formic acid — water binary system.
Dobe there a name for this phenomenon? Temporary2 - 3-4-2011 at 15:41
I'm new here but I have used boron oxide followed by distillation atmospherically to remove water from formic acid. Large scale I'm sorry but 8 kg
85% formic acid to 2.5 kg B2O3. Reflux overnight and distill to give dry formic aid. I use it at work to make anisyl formate from anisyl alcohol
using a mixed anhydride of acetic and formic acid.Cou - 4-12-2019 at 16:31
Copper (ii) sulfate works for drying acetic acid, maybe it could work for formic acid too.
Boron oxide can be purchased on amazon, sold by chemsavers
[Edited on 5-12-2019 by Cou]Boffis - 5-12-2019 at 01:22
The best laboratory method for high test formic acid preparation is azotropic distillation with heptane or similar boiling range petroleum ether until
you get the acid to >90% and then use a free-thaw method (the frozen crystals are richer in formic acid than the liquid). Starting with 85% acid
which is easily available and assuming you have a decent size freezer by recycling the residues this process is quite efficient though a bit of a ball
ache. Both techniques are covered in several publication and patents. This may not be the most efficient process industrially but from an amateur
perspective it is probably the best.Cou - 5-12-2019 at 10:30
